1. Field Of The Invention
The present invention relates to the manufacture of wrappers for smoking articles such as cigarettes. More particularly, this invention relates to the use of gels produced by a solution-gelation or "sol-gel" process for controlling the combustion of wrappers for smoking articles. In one embodiment, the gels made by this process are applied as coatings to paper fibers before the paper is formed into wrappers for smoking articles. The coated paper wrappers of this invention are useful in reducing or preventing combustion of the wrappers of smoking articles. The wrappers are also useful in controlling the mass burn rate of cigarettes.
2. Description Of Related Art
One problem with smoking articles such as cigarettes is the amount of sidestream smoke generated during burning. Sidestream smoke is the smoke generated by cigarettes when they are burning but not being drawn upon by the smoker, as when a cigarette is placed in an ashtray between puffs. Sidestream smoke may be objectionable to non-smokers.
Efforts have been made to reduce the amount of sidestream smoke generated by cigarettes. While these methods may reduce the amount of sidestream smoke, they do not provide the smoker with a cigarette that looks, feels, and tastes the same as conventional cigarettes.
U.S. Pat. No. 4,231,377 to Cline et al. ("Cline I") refers to a method of reducing sidestream smoke by applying a specified amount of magnesium oxide or magnesium hydroxide in combination with specific chemical "adjuvants" to paper fibers as a filler or coating. The magnesium salts are applied as a solution. However, according to U.S. Pat. No. 4,433,697 to Cline et al. ("Cline II"), the ash generated by burning cigarettes made from paper prepared according to the method of Cline I is unacceptable because of its flakiness. Cline II proposes to reduce the flakiness of the ash by adding ceramic fibers to the paper-making slurry. The method of Cline II is problematic because of the substantial cost of the ceramic fibers. A further shortcoming of the proposal of Cline II is that ceramic fibers must be added to the paper-making slurry; commercially available cigarette papers cannot be modified according to the proposal after their manufacture.
U.S. Pat. No. 4,450,847 to Owens refers to the use of fine particle size magnesium hydroxide gel in place of the magnesium hydroxide referred to in Cline I and II. Although Owens characterizes his magnesium hydroxide as a gel, he states that the gel is actually "an apparently homogeneous substance or a dispersion consisting of an aggregate of very small particles in very close association with a liquid, and the gel at the concentrations used in this invention is actually broken into flocs floating in the aqueous medium." (Col. 3, lines 62-68). Owens' magnesium hydroxide gel is said to be used with magnesium oxide or calcium carbonate and a suitable chemical "adjuvant" as in Cline I and II.
Hampl et al., U.K. Patent Application GB 2 191 930 A, refers to cigarette papers that have been formed with high superficial surface area fillers. These cigarette papers are stated to yield reduced sidestream smoke when used as wrappers for cigarettes. Fillers such as attapulgite clay, fumed or activated alumina, chalk, fumed silica, and peroxides of magnesium, calcium, and strontium are said to be useful. Other fillers such as the carbonates, phosphates, sulphates, aluminates, and silicates of certain metals are also said to be useful as long as their superficial surface area exceeds 20 m.sup.2 /g. Hampl et al's method also requires the use of potassium or sodium salts of various acids to maintain the integrity of the cigarette ash.
Apart from the problems already noted, the modified wrappers of Cline I and II, Owens, and Hampl et al. all suffer from a serious disadvantage --the smoking of cigarettes made from paper containing magnesium oxide or magnesium hydroxide produces an off taste. It is believed that this taste arises from the strongly alkaline nature of the magnesium and from the other chemicals used.
In addition, the size of the particles employed by Cline I and II, Owens, or Hampl is critical. If the particles are too small, they will be dislodged from the wrapper, creating an objectionable dust. If they are too large, they will obstruct the porosity of the wrapper, interfering with the combustion of the tobacco fuel rod.
Accordingly it is an object of this invention to provide a wrapper for smoking articles which reduces or prevents combustion of the wrappers of smoking articles and which may be incorporated into a smoking article which has the look, feel, and taste of conventional smoking articles.